Underground fluid storage in permeable formations

ABSTRACT

Fractures in caprocks of fluid storage reservoirs can be sealed and flow barriers can be established at desired regions of porous rocks by locally freezing the formation water to form an impervious cryogenic structure and/or by forming gas hydrates by contacting hydrate forming gases with formation water subjected to heat removal therefrom and agitation, for the purpose of stored fluid leakage control, increasing storage volume of limited reservoirs, and formation of storage conditions in homoclines and monoclines.

United States Patent [72] Inventors James F. Ralstin; 2.991.624 7/1961Closs et a1 61/.5 Jack H. Heathman, 672 Union Center 3,152,640 10/ 1964Marx 166/273X Building, Wichita, Kans. 67202 3,175,614 3/1965 Wyl1ie..166/305X [21] Appl. No. 726,720 3,295,328 1/1967 Bishop 61/.5 [22] Fil dMay 6, 1968 3,344,607 10/1967 Vignovich 611.5 [45] Patented Feb. 2, 19713,379,260 4/1968 166/292X 3,393,738 7/1968 166/309X 3,477,509 1 1/ 1969l66/274X [54] UNDERGROUND FLUID STORAGE 1N PERMEABLE FORMATIONS PrimaryExaminer-Stephen J. Novosad 0 Claims 9 Drawing Figs. Attorney-John H.WlddOWSOn [52] U.S.Cl 166/281,

166/27 166/305 ABSTRACT: Fractures in caprocks of fluid storagereservoirs [51] Int. Cl E2lb 33/138, can besealed and n barriers can beestablished at desired E2lb43/26 regions of porous rocks by locallyfreezing the formation [50] Field of Search 166/285, water to f n irvious cryogenic structure and/or by (305D 2715 61/5 forming gashydrates by contacting hydrate forming gases with [56] Reerenm Citedfonnation water subjected to heat removal therefrom and agitation, forthe purpose of stored fluid leakage control, in- UNITED STATES PATENTScreasing storage volume of limited reservoirs, and formation 2,777,6791/1957 Ljungstrom l66/302X of storage conditions in homoclines andmonoclines.

PATENIED FEB 2 |97l 3,559; 737 I sum 1 or 2 I7 F/GI 4 INVENTOR.

JACK H. HEATHMAN BY JAMES F. RALSTIN ATTORNEYS UNDERGROUND FLUID STORAGEIN PERMEABLE FORMATIONS This invention relates to the undergroundstorage of fluids. In one aspect it relates to the underground storageof gaseous fluids. In another aspect it relates to a localized in situfreezing process whereby an impervious cryogenic structure is formed toseal fractures in the caprock of a permeable formation containing storedfluids. In another aspect it relates to a localized in situ freezingprocess whereby an impervious cryogenic structure is formed at astrategic location, to enlarge the available storage volume. In yetanother aspect it relates to a method of forming a gas hydrate, in situ,in order to seal fractures in formations and the like in the caprock toprevent the undesired migration of the stored fluid out of the permeableformation. In another aspect it relates to a method of forming gashydrates within a porous formation to enlarge the availa-' ble fluidstorage volume within the porous rock.

In recent years much attention has been directed to underground storageof fluids, especially to the storage of volatile fluids such ashydrocarbon fuels. Due to the varying seasonal demands for hydrocarbonfuels much work has been done in discovering methods of storing thesefuels. However, many of the prior art methods utilize methods of formingcaverns and the like by mining or dissolving a cavity in a solublestrata. Such caverns are limited by size and economics.

Other prior art methods have utilized surface reservoirs wherein thefluids are stored within a vessel or reservoir having a cap or coverover the reservoir. The fluids are then maintained at a temperaturesufficiently low so that the vapor pressures of the fluids will notexceed pressures which the cap cover is designed to withstand. For largevolume storage such methods of utilizing surface reservoirs areundesirable due to the expense in constructing the reservoirs and thenecessity of requiring a portion of the surface of the land in order toprovide for such storage. Thus, means are constantly being soughtwhereby fluids can readily be stored in natural formations of the earthwhich are economical to use, and which will yield, on recapture, adesirable quantity of the product stored within the formation.

Other prior art methods have utilized underground fluid storage whereinthe fluid is stored in large quantities of porous and permeable rock atvarious depths beneath the surface of the earth. Such undergroundstorage is especially feasible in geographic areas having depleted orsemidepleted oil and gas reservoirs which can be converted into fluidstorage fields. In areas devoid of depleted or semidepleted fields,aquifer/aquiclude systems associated with structural and/orstratigraphic traps can be converted to fluid storage reservoirs. Thesesystems are called aquifer storage facilities.

In the utilization of the underground storage facilities leakage fromthe storage reservoirs to higher porous and permeable rock bedsfrequently occurs through fractures or breaks in the caprock, throughnonsealing faults, and the like. Sometimes it is feasible to collectleaking fluids from wells completed in the higher rock beds and cyclethe fluids back to the storage formation. However, leakage control byfluid cycling is an economic burden on the operation. Thus, othermethods of fluid leakage control are highly desirable.

Several methods for soil and porous rock impermeation are known in theprior art wherein grout is employed to seal the fracture or break in thecaprock. However, the success of the grouting depends on the completeinvasion of the grout into the fracture channels, pores, and porechannels of the rock body which is to be impermeated. Due to the verynature of the rock structure a complete invasion of the leakage channelby the grout is frequently not achieved. Thus, the prior art methodswhich employ the grouting technique many times are undesirable.

Even when a desirable fluid storage reservoir is located having ananticlinal trap surrounded by structural conditions suitable for fluidstorage, the reservoir is frequently limited in storage capacity by asaddle region or spill point. The capacity of such a reservoir can beincreased if gas migration beyond the saddle region is prevented byregional impermeation of the storage formation.

Further, frequently structural conditions favorable to fluid storagecannot be found near population centers, even though various porous andpermeable rocks overlain by impervious formations are encountered belowthe ground. Thus, it is very desirable to provide a means to modify theunderground structural conditions so that a reservoir is formed whichcan be utilized for the underground storage of fluids thus providing asupply source near the population centers. Thus, it is highly desirableto provide a method wherein the structurally high end of the porous rockbed, the outcropping end, can be impermeated thus producing a desirablereservoir for the underground storage of the fluid.

According to the present invention, a method is provided forimpenneating an underground formation for sealing fractures in theporous rock and/or its caprock, by removing heat from the rocks and thesaturating water, thus causing the water to crystallize and form asubstantially impervious cryogenic structure.

Further according to the invention, a method of rock impermeation andchannel sealing is provided whereby the formation water is cooled andcontacted with a gas capable of forming gas hydrates so that asubstantially impervious rock hydrate structure is formed thereby.

Further, a method is provided for sealing fractures and/or brokenformations in the upper impervious caprock covering a porous geologicalstructure by removing heat from the aquifer and/or aquiclude water andthus producing localized cooling of the same so that an imperviousstructure is formed which seals the broken or fractured caprockstructure.

Further according to the invention, a method is provided whereinlocalized cooling of aquifer water is employed to form gas hydrates inthe rock pore spaces in order to employ the hydrates so formed to sealthe broken and/or cracked formations within the caprock covering thedesired storage area.

Further, according to the invention, a method is provided wherein theheat flow through porous rocks and saturating fluids is employed toinitiate and maintain localized in situ freezing so that the aquiferand/or aquiclude water is crystal lized and an impervious cryogenicstructure is formed.

Further according to the invention, a method is provided whereby thefluid storage capacity of the structure can be increased by means ofinitiating and maintaining a localized in situ freezing process wherebythe water in the aquifer and/or aquiclude is crystallized and animpervious cryogenic structure similar to a dam is formed across thesaddle region of the structure.

Drawings accompany and are a part of this disclosure. These drawingsdepict preferred specific embodiments of the underground storage inpermeable formations of the invention, and it is to be understood thatthese drawings are not to unduly limit the scope of the invention. Inthe drawings,

FIG. I is a plan view of a portion of the ground surface intended toillustrate the manner in setting out a method of this invention inpreparing for the construction of a flow barrier in a porous andpermeable formation or to repair fractures or breaks in its caprock;

FIG. 2 is a cross section of the surface of the earth taken along theline 2-2 of FIG. 1 illustrating the application of the method of thisinvention to form a flow barrier to enlarge the fluid storage area of anunderground structure and to seal fractures or breaks in the caprockabove the formation being employed for fluid storage;

FIG. 3 is a cross section taken along the line 3-3 of FIG. 1illustrating the formation of a barrier according to the presentinvention;

FIG. 4 is a cross section taken along the lines 4-4 of FIG. 1illustrating the sealing of a fracture system in the caprock and thelike above the formation being employed for fluid storage;

FIG. 5 is a cross-sectional view of the earth depicting a typicalhomocline showingthe formation of storage conditions by localimpermeation methods of the present invention;

FIG. 6 is a cross section of the earth of a typical anticline showingthe use of directionally drilled wells for in situ formation freezingand/or for forming a hydrate according to the present invention;

FIG. 7 is a structural contour map of a typical anticline showing theplacement of gas hydrate flow barriers to seal fractures in a caprockand to enlarge a reservoir by the formation of a damlikc barrier in thestorage formation;

FIG. 8 is a schematic cross-sectional view illustrating a heat sink wellmeans employed by the process of the present invention;

FIG. 9 is a schematic cross-sectional view of a refrigerant circulationsystem used according to the process of the present invention.

In the following is a discussion and description of the invention madewith reference to the drawings whereupon the same reference numerals areused to indicate the same or similar parts and/or structure.

The discussion and description is of preferred specific embodiments ofthe new process of our invention for forming formations of our inventionfor storing fluids underground, and it is to be understood that thediscussion and description is not to unduly limit the scope of theinvention.

Referring now to FIG. 1, a plan view of a portion of the ground isillustrated having contour lines 11 which indicate a saddle region 12across which a barrier structure, 14, is to be constructed and a crestregion 16 which has a fracture system or breaks therein which is to besealed by local impermeation 17. In preparation for building barrier 14in saddle region 12 the present method can be applied by drilling andcompleting a series of wells 18 at suitable intervals so that wells 18form a line which transverses the saddle region 12. The bottom portionof wells 18 are positioned within the aquifer zone which will bediscussed in detail hereinafter. Likewise, in preparation for theforming of impervious structure 17 to seal the fractures or breaks inthe caprock covering the crest of the anticline 16 the present methodmay be applied by drilling and completing a series of wells 19 atsuitable intervals so that wells 19 fonn a line which approximatelyfollows the system of the fractures or breaks in the caprock. The bottomportion of wells 19 are positioned in the caprock in the immediatevicinity of the fractures or breaks in the caprock as will be discussedhereinafter.

Referring now to FIG. 2 a cross-sectional view of the ground taken inlines 2-2 of FIG. 1 is illustrated. Underground structure or formation21 is shown comprising an aquifer zone 22, such as sandstone, having anaquiclude zone 23, or a caprock zone, such as limestone, positioned ontop of aquifer zone 22. Likewise, a sufiiciently impervious lower layeraquiclude zone 24, such as dolomite, is positioned below aquifer zone22. Aquifer zone 22 is the prospective fluid storage formation. However,it should be understood that other types of impervious substances canmake up the impervious zones which are positioned above and belowaquifer zone 22. Other types of impervious materials which can serve asthe caprock which covers the prospective storage formation are wellknown in the field of geology.

An aquifer as used herein is defined as a water-bearing bed of stratumof underground porous and permeable rock, sand, or gravel. In order forthe formation to serve as a reservoir for fluid storage use, such as gasstorage, the aquifer must be over- Iayed by beds of a sufficientlyimpervious aquiclude or caprock through which stored fluids cannotescape.

Referring now to FIG. 2 in conjunction with FIG. I, aquifer zone 22 isoverlain by impervious aquiclude zone 23 and underlain by imperviousaquiclude zone 24 and is associated with a doubly-plunging asymmetricalanticline. The anticline considered for fluid storage joins a largeranticlinal structure through saddle region 12. However, the anticlinehas a limited storage capacity because its structural closure is limitedby saddle region 12. Further, aquiclude zone 23 has a localized fracturesystem 26 near its crest, and thus allows fluids stored therein toreadily escape and as such is highly undesirable. Fracture system 26near the crest of aquiclude zone 23 can be discovered by geophysicaland/or nonsteady water pumping tests, tracer surveys, and the like whichare well known. Once fracture system 26 in aquiclude zone 23 isdiscovered fracture system 26 must be sealed if the reservoir is to beutilized for fluid storage in aquifer zone 22. Likewise. it is desirableto form an impervious structure, such as barrier 14, across saddleregion 12 to prevent the movement of stored fluids from passing beyondthe saddle region of the formation and thus increase the storagecapacity of aquifer zone 12. Thus, by the method of the presentinvention of utilizing in situ freezing to crystallize the aquicludewater to seal the flow channels of fracture system 26, fluids storedwithin aquifer zone '22 are prevented from escaping through the fracturesystem. Likewise, by crystallizing aquifer water within saddle region 12an impervious wall structure, such as barrier 14, is formed and themovement of storedfluids is restricted thus enlarging the capacity ofaquifer zone 22 so that a larger volume can be utilized for the storageof fluids therein. 7

Referring now to FIG. 3 in conjunction with FIG. 2 the method of formingthe barrier 14, across saddle region 12 of underground formation 22 willbe discussed. A plurality of wells 18 are completed in aquifer zone 22and used as lower temperature heat sinks relative to the surroundings inorder to crystallize aquifer water and form a cryogenic structure 14 inaquifer zone 22 up to the desired distance away from each of wells 18.Such can be accomplished by pumping a coolant, such as a refrigerant,down to the bottom of wells 18 by pump units 27. As is readily apparent,the barrier 14 is constructed by in situ crystallizing of the aquiferwater in aquifer zone 22. Cryogenic rock-water structure 14 preventsfluid migration beyond saddle region 12 and thus increases the storagecapacity of aquifer zone 22 by lowering the extreme spill point of theformation. Thus, it is readily apparent that without the use ofcryogenic barrier 14 fluid storage in aquifer zone 22 is confined, asviewed from the top, within contour lines 260 (see FIG. 1) whereincontour line 260 denotes points on the top of aquifer zone 22equidistant and vertically from a reference plane, such as sea level,measured in feet. However, with the formation of cryogenic barrier 14the capacity of formation 22 is increased by extending the gas-waterinterface to contour line 300. Thus, by employing the method of formingan in situ cryogenic barrier across the saddle region of the formationthe total fluid storage capacity of the aquifer zone is greatlyenlarged.

Referring now to FIG. 4, in conjunction with FIG. 2, the method ofsealing fracture system 26 in aquiclude zone 23 will be discussed. Aplurality of wells 19 are completed in aquiclude zone 23 which overlaysaquifer zone 22 which is to be utilized for fluid storage, such asnatural gas storage. When fracture system 26 is found to be present inaquiclude zone 23, and it is desired to utilize aquifer zone 22 fornatural gas or other fluid storage, fracture system 26 must be sealed.Wells 19 are set a desired distance apart and are positioned so as tosubstantially follow the line of fracture system 26. When wells 19 arecompleted a coolant, such as a refrigerant, is pumped down the wells bypump units 27. The refrigerant cools the formation and the aquifer andaquiclude water is frozen in situ thus fonning a cryogenic structure 17which seals fracture system 26 and thus prevents the stored fluids fromescaping aquifer zone 22 through fracture system 26.

Referring now to FIG. 5, structural formation 29 which can be modifiedby the present invention and thus made into a suitable fluid storagereservoir is illustrated. In this situation the present inventioninvolves the establishment of favorable storage conditions in porous,permeable formation 31 of a homocline or monocline in which successivelyyounger rock strata dip away from a central uplift, and in the case of ahomocline are gently curved in a direction perpendicular to thedirection of the dip. When such a formation as formation 29 is overlainby a successively impervious formation 32, a cryogenic structure 14canbe developed in permeable formation 31 by completing a plurality of heatsink wells 18 at a desired vertical distance from the surface of theground so that a refrigerant can be pumped into wells 18 by pump unit 27and thus cool the formation and crystallize the water to seal theoutcropping or upper end of permeable fonnation 31. Depending upon thedegree of dip, the thickness of permeable formation, and the fluidstorage capacity desired it may be desirable and necessary to locategeological conditions where the permeable bed is also underlain by animpervious formation, such as formation 33.

Referring now to FIG. 8, a schematic of the proposed heat sink wells 18and I9 employed according to the present invention are shown. A suitablerefrigeration system. such as a vapor compression refrigeration system,can be used to pump an appropriate refrigerant such as a freon. COliquified petroleum gas (LPG), and the like, down an insulated tubing34, to produce a cooling effect to freeze the water of the aquifersurrounding the well bore. When the refrigerant reaches the last jointof tubing 34 it is throttled by a throttle means 36, so that some of therefrigerant flushes into vapor during the throttling process. Theremainder of the refrigerant evaporates inside the bottom section ofcasing 37 by extracting heat from the rock matrix and water or ice inthe pore spaces, and the evaporated refrigerant flows up through theannulus between insulated tubing 34 and of the insulated long stringcasing 37, and enters compressor 38 as a saturated or superheated vaporat low pressure. Following compression it rejects heat in a condenserand begins its cycle down tubing 34 again. The string of casing 37 ispreferably thermally insulated from the formations above the storageformation by an insulation material, such as an organic or inorganicliquid, and the insulation material is placed between the long string ofcasing 37 and short strings of outer casing 39 above packer 41 but belowChristmas tree 42. Low temperature resistant high strength cement 43 isemployed to bind the casing strings to the fonnation through the caprockand the storage zone. The annular space between the overlying beds andthe outer casing string is filled with casing pack material 44 which arewell known in the drilling art and as such are believed sufficientlywell known. Surface conductor casing 46 is cemented with lowtemperatures being considered. In some areas intermediate strings ofcasings may be necessary and in others it may be possible to eliminatethe outer string of easing completely and insulate only the long stringof easing from formation by using low conductivity casing packs abovethe cement top. However, such will vary widely depending upon the areawherein the formation is located, the depth of the formation, and thetype of the formation.

The spacing and the number of wells 18 and 19, the refrigerant type andcirculation rates, the duration of time for the propagation ofapproximately egg-shaped water crystallizationand final merging into animpervious cryogenic rockwater structure, depend upon a multitude offactors, such as chemical, mechanical, thermoproperties of theformation, and the in situ water, structural conditions, formationtemperature, formation pressure, and the like. Obviously, the method ofporous rock freezing requires close welded spacing, such as measured intens of feet.

Referring now to FIG. 6 a plurality of wells 47 are illustrated whichhave been drilled by a directional drilling process in order to providegreater contact area between the formation of interest and heat sinkwells 47. However, the use of directionally drilled wells 47 will dependupon the depth of the formation and its structural attitude. Thus, thedecision to employ direction drilling in order to provide heat sinkwells would depend on the circumstances throughout the reservoir beingprepared.

Referring now to FIG. 9 a refrigerant circulation system for forming acryogenic structure according to the present invention is depicted whenit is desirable to employ wider well spacing. A line of refrigerantinjection wells 48 and withdrawal wells 49 are drilled into the aquiferor aquiclude zone where the water-rock system is to be locally frozen.Injection wells 48 and withdrawal wells 49 are cased through theformation of interest and perforated selectively at a levelcorresponding to an approximately half way point between the top and thebottom of the cryogenic structure to be fonned. By this limited entryperforation technique, selective fracturing at each well, designated bynumeral 51, flow channels 52 of least resistance are established betweenany pair of injection wells 48 and withdrawal wells 49. The liquidrefrigerant is pumped by pump 53 through conduit 54 into tubing 56 ofinjection wells 48 and withdrawn by submergible pumps 57 located in eachwithdrawal well 49 together with formation water. The liquid refrigerantand the formation water is then pumped up tubing 58 and through conduit59 and into pump means 53. The cycling of refrigerant through theformation between the wells is first carried on without cooling and heatrejection at the surface. The purpose of first cycling the refrigerantthrough the formation without cooling is to saturate flow channels 52formed by hydraulic fracturing of the rock matrix immediatelysurrounding the flow channels with refrigerant. During the refrigerantcirculation process at normal temperatures the water cut of therefrigerant withdrawn from the formation will steadily decline to anegligible level or it will stabilize. Water is removed at the surfaceby separators, (not shown), and the separated refrigerant is sent to acondenser to begin another cycle. When the water cut stabilizes at a lowvalue, the refrigerant is gradually cooled at pump 53. The refrigerantpicks up heat from high temperature heat sources, i.e., the for mationrock matrix and water, while it flows through the channels of theformation, and it rejects heat at the low temperature heat sink, thesurface separation and refrigeration systems. A refrigeration plant suchas a vapor pressure refrigeration plant can be employed to cool therefrigerant circulating through the formation.

When the temperature of the refrigerant in the flow channels is reducedbelow the freezing point of the formation water, the cryogenic structurebegins to form, and the interface between the ice region and the coldwater region propagates away from the flow channels. Since therefrigerant saturates the flow channels but does not freeze at theoperating pressure and temperature of the system, it continues tocirculate between pairs of wells, such as injection wells 48 andwithdraw wells 49. Thus, the refrigerant acts as a low temperature heatsink relative to the formation.

The refrigerant employed by the above-mentioned process can be anysuitable refrigerant which is known in the art. However, it is preferredthat the refrigerant selected be water immiscible having a density equalto or slightly less than the density of the formation water and aviscosity higher than the viscosity of the formationwater. Further, therefrigerant should be in the liquid phase during its injection into thewells and its flow through the formation and have high heatconductivity. The requirement of the viscosity of the refrigerant beinghigher than the viscosity of the formation water is a compromise betweenminimization of viscous fingering and high pumping costs required todeliver the refrigerant to the bottom of the input wells and thus intothe formation. The method of utilizing a series of refrigerant injectionwells and refrigerant withdrawal wells has a definite advantage over thebefore-mentioned heat sink well method, wherever applicable, in that theutilization of the refrigeration injection wells and withdrawal wellsprovide greater area of exposure between the heat source and the heatsink, and utilizes both conduction and convection heat transferprinciples.

Refrigerant injection wells 48 are equipped with insulated tubing 56 andare isolated thermally from the main body of casing 61 by an organic orinorganic insulating material which is placed in the annulus above thecasing to tubing packer 62. Casing 61 is cemented 63 up to a desiredpoint above the caprock, and the formation to casing annulus above thecement top is filled with casing-pack material of low heat conductivity64. The surface conductor casing and the intermediate strings of casingare not shown for the sake of simplicity but are well known in thedrilling art.

Refrigerant withdrawal wells 49 are also equipped with the insulationlined tubing 58, submergible pumps 57, well control equipment 66, andsurface flow lines or conduits 59. Refrigerant withdrawal wells 49 canbe completed with one string of casing 67 cemented to the storageformation and the aquifer zone and isolated from other formations byinsulating casing-pack 68. Likewise, a construction similar to the heatsink wells shown in FlG. 8 can be used for increased protection from thepossibility of leakage of the circulating fluids and for providingbetter thermal insulation from the strata above the storage formationand its caprock. lnterrnediatc and surface conductor casing strings arelikewise not shown for the sake of simplicity.

Following the stabilization of the water out and the freezing of thewater surrounding the refrigerant flow paths in the formation, one mayremove the submergiblc pumps from the withdrawal wells, and thus rely onthe surface pumps, to circulate the refrigerant at sufficient flow ratein order to maintain the cryogenic rock structure so formed within theboundaries determined by design and subsurface conditions.

Referring now to FIG. 7, another embodiment of the present inventionwill be discussed which also employs the removal of heat from theformation and the formation water surrounding the area wherein the insitu formed barrier is to be constructed in order to seal a fracture inthe caprock or enlarge the total area which can be employed for storageof fluids by the continuation of a barrier in the saddle region of theformation as previously discussed with reference to FlGS. 1 and 2.Certain gases such as C0,, H28, 80 and natural and manufactured gasesconsisting chiefly of light parafinic hydrocarbons form solid gashydrates when the gases come into contact with water in sufficientamounts when certain conditions as to temperature and pressure exist. Itis known that the gas hydrates are formed at temperatures above thefreezing temperature of the water.

Hydrocarbon hydrates are solid solutions of the hydrates of lowerhydrocarbons which are capable of forming hydrates. High velocity,turbulance, pressure pulsations additives such as alcohol or aceticacid, and inoculation of small hydrate crystals accelerates the hydrateformation. It has also been found that the formation of gas hydrateswith ice proceeds at a negligible rate.

A local gas hydrate barrier to fluid flow can be developed in porous andpermeable bodies suitable for fluid storage by bringing low temperaturewater into contact with a hydrate forming gas, under favorabletemperature, pressure and agitation conditions. For example, thetechnique of impenneation by gas hydrate 71 can be used to seal fracturesystem 26 in caprock 23 of underground stnicture 21 shown in FIGS. 2 and7, to form barrier 14 at anticline saddle region 12, of aquifer zone 22.Likewise, gas hydrate 71 can be utilized to form the flow barrier inporous beds on a homocline or monocline (see FIG. 5). If the localimpermeation is not necessary until the stored gas approaches the zoneof leakage or spill, the gas front can be brought into contact with acold water zone maintained by circulating chilled water between pairs ofinjection and withdrawal wells 48 and 49, respectively, so that hydratesare formed in situ.

If the stored gas is one which does not form gas hydrates, or if thelocal impermeation is to accomplished before the stored gas approachesthe leakage or spill zone, other gas, such as CO, or light hydrocarbonscan be injected into the formation through additional injection wells toprovide hydrate forming gas. These gas injection wells are locatedbetween the approaching front of the stored gas and the line of coldwater circulation wells 48 and 49.

Injection wells 48 and withdrawal wells 49 for cold water circulationcan be similar to the refrigerant cycling system depicted in FIG. 9 withthe exception that the circulating refrigerant is the formation waterchilled at the surface and hydraulic fracturing of the formation betweenthe wells may or may not be necessary. The circulation of the water athigh rates between the wells is for the purpose for creating agitationin the formation in addition to the local cooling of the porous rocksand the contents of its pores. Thus, by the cooling effect so created,coupled with the agitation in the formation the gas hydrates of the gasare formed. The steam-jet refrigeration techniques are especiallysuitable to chill the water at the surface facilities.

Thus, it is readily apparent that by utilizing the method of the presentinvention of porous media impermeation by in situ freezing of native oradded water, and by gas hydrate formation desirable results can beobtained wherein underground storage of fluids can be achieved inprospective storage reservoirs with locally'fractured caprocks and/orlimited by saddle regions. Likewise, the method for sealing fracturesand forming the barrier structure of the invention is by no meanslimited to the control of leakage or spill conditions in gas storagereservoirs. Rather, the method can be utilized whenever and whereverporous and impermeable rocks are to be locally impermeated to fluid flowand the economics and technical feasibility of the application isascertained.

Thus, the foregoing discussion and description is made in connectionwith preferred specific embodiments of the method of underground storagein porous media of the invention. However, it is to be understood thatthe discussion and description is only intended to illustrate and teachthose skilled in the art how to practice the invention and such is notto unduly limit the scope of the invention which is defined in theclaims set forth hereinafter.

We claim:

1. A method for locally impermeating a naturally occurring undergroundformation to be used for gaseous fluid storage having a porous,permeable aquifer zone overlain by an impervious aquiclude zone having afracture therein or having an escape path thereunder making suchunsuitable for fluid storage, so that said aquifer zone can be utilizedfor storage of fluids without said fluids escaping from said aquiferzone comprising, subjecting said formation to a coolant in the region ofsaid fracture or escape path as the case may be, thereby removing heatfrom said fonnation and fonning a barrier structure adjacent the area ofsaid formation where said formation is subjected to the flow of saidcoolant, thereby providing a gaseous fluid storage reservoir.

2. The method according to claim 1 wherein said coolant is a refrigerantwhich is substantially water immiscible, has a density equal to or lessthan the density of water in said formation, has a viscosity higher thanthe viscosity of said water in said formation, is present in a liquidphase during injection into said fonnation, and possesses a high heatconductivity.

3. The method according to claim 2 wherein said aquifer zone issubjected to said refrigerant and said refrigerant is selected from thegroup consisting of carbon dioxide, freon, and the like, saidrefrigerant being continuously circulated down to said formation andback to the surface, and said barrier is a cryogenic structure formed inthe area where said refrigerant is contacted with water in said aquiferzone.

4. The method according to claim 2 wherein said coolant is directlycontacted with said formation.

5. A method for locally permeating an underground formation to be usedfor fluid storage having a porous, permeable aquifer zone overlain by animpervious aquiclude zone having a fracture and water therein so thatsaid aquifer zone can be utilized for storage of fluids without saidfluids escaping from said aquifer zone comprising, subjecting saidaquiclude zone to a refrigerant which is substantially water immiscible,has a density equal to or less than the density of the water in saidformation, has a viscosity higher than the viscosity of said water insaid formation, is present in a liquid phase during injection into saidformation, and possesses a high heat conductivity selected from thegroup consisting of carbon dioxide, freon, and the like, therebyremoving heat from said formation and forming a barrier structure, saidbarrier being an impervious structure formed where said refrigerant iscontacted with said water in said aquiclude zone thus sealing saidfracture in said aquiclude zone.

6. A method for locally impermeating an underground formation to be usedfor fluid storage having a porous, permeable aquifer zone overlain by animpervious aquiclude zone so that said aquifer zone can be utilized forstorage of fluids without said fluids escaping from said aquifer zonecomprising, selectively hydraulically fracturing said formation toestablish flow channels of least resistance in said formation.subjecting said formation to a coolant thereby removing heat from saidformation and forming a barrier structure adjacent the area of saidformation where said formation is subjected to the flow of said coolant.V

7. A method for locally impermeating an underground formation to be usedfor storing hydrate forming gases having a porous, permeable aquiferzone overlain by an impervious aquiclude zone so that said aquifer zonecan be utilized for storage of fluids without said fluids escaping fromsaid aquifer zone comprising, subjecting said formation to cooled water,said water being contacted and admixed with said hydrate forming gases,thereby removing heat from said formation and fonning a gas hydratebarrier structure adjacent the area where said formation is subjected tothe flow of said water.

8. The method according to claim 7 which includes the step of injectinga hydrate forming gas selected from the group consisting of carbondioxide, hydrogen sulfide. sulfer dioxide, natural and manufacturedgases having a high content of light parafinic hydrocarbons. and thelike, prior to the injection of said fluid to be stored in saidformation, admixing said gas hydrate forming gas and said cooled waterthus forming a gas hydrate barrier structure.

9. The method according to claim 8 which includes admixing an additiveselected from the group consisting of alcohols, acetic acid, and thelike to said hydrate forming gas to accelerate hydrate formation in saidformation.

10. The method according to claim 9 wherein said cooled water iscontinuously circulated down to said formation and back to the surfacethus maintaining cooled water within the formation at all times.

2. The method according to claim 1 wherein said coolant is a refrigerantwhich is substantially water immiscible, has a density equal to or lessthan the density of water in said formation, has a viscosity higher thanthe viscosity of said water in said formation, is present in a liquidphase during injection into said formation, and possesses a high heatconductivity.
 3. The method according to claim 2 wherein said aquiferzone is subjected to said refrigerant and said refrigerant is selectedfrom the group consisting of carbon dioxide, freon, and the like, saidrefrigerant being continuously circulated down to said formation andback to the surface, and said barrier is a cryogenic structure formed inthe area where said refrigerant is contacted with water in said aquiferzone.
 4. The method according to claim 2 wherein said coolant isdirectly contacted with said formation.
 5. A method for locallypermeating an underground formation to be used for fluid storage havinga porous, permeable aquifer zone overlain by an impervious aquicludezone having a fracture and water therein so that said aquifer zone canbe utilized for storage of fluids without said fluids escaping from saidaquifer zone comprising, subjecting said aquiclude zone to a refrigerantwhich is substantially water immiscible, has a density equal to or lessthan the density of the water in said formation, has a viscosity higherthan the viscosity of said water in said formation, is present in aliquid phase during injection into said formation, and possesses a highheat conductivity selected from the group consisting of carbon dioxide,freon, and the like, thereby removing heat from said formation andforming a barrier structure, said barrier being an impervious structureformed where said refrigerant is contacted with said water in saidaquiclude zone thus sealing said fracture in said aquiclude zone.
 6. Amethod for locally impermeating an underground formation to be used forfluid storage having a porous, permeable aquifer zone overlain by animpervious aquiclude zone so that said aquifer zone can be utilized forstorage of fluids without said fluids escaping from said aquifer zonecomprising, selectively hydraulically fracturing said formation toestablish flow channels of least resistance in said formation,subjecting said formation to a coolant thereby removing heat from saidformation and forming a barrier structure adjacent the area of saidformation where said formation is subjected to the flow of said coolant.7. A method for locally impermeating an underground formation to be usedfor storing hydrate forming gases having a porous, permeable aquiferzone overlain by an impervious aquiclude zone so that said aquifer zonecan be utilized for storage of fluids without said fluids escaping fromsaid aquifer zone comprising, subjecting said formation to cooled water,said water being contacted and admixed with said hydrate forming gases,thereby removing heat from said formation and forming a gas hydratebarrier structure adjacent the area where said formation is subjected tothe flow of said water.
 8. The method according to claim 7 whichincludes the step of injecting a hydrate forming gas selected from thegroup consisting of carbon dioxide, hydrogen sulfide, sulfer dioxide,natural and manufactured gases having a high content of light parafinichydrocarbons, and the like, prior to the injection of said fluid to bestored in said formation, admixing said gas hydrate forming gas and saidcooled water thus forming a gas hydrate barrier structure.
 9. The methodaccording to claim 8 which includes admixing an additive selected fromthe group consisting of alcohols, acetic acid, and the like to saidhydrate forming gas to accelerate hydrate formation in said formation.10. The method according to claim 9 wherein said cooled water iscontinuously circulated down to said formation and back to the surfacethus maintaining cooled water within the formation at all times.